Influence of trace-metal availability on anaerobic redox progression

Trace-metal availability has fluctuated substantially throughout Earth’s history and has likely influenced microbial metabolic activity by regulating the functions of redox-active enzymes involved in anaerobic metabolism (Giovannelli, 2023; Mele et al., 2023; Jelen et al., 2016). Since microbial processes such as hydrogen oxidation, nitrate reduction, sulfate reduction, and methanogenesis are tightly linked with biogeochemical cycling, variation in the availability of specific metals may alter the rate and trajectory of anaerobic redox progression (Kolb et al., 2017; Teng et al., 2019). In this preliminary study, anoxic hydrothermal brine microcosms collected from a shallow hydrothermal vent were used to investigate how contrasting trace-metal regimes influence anaerobic redox metabolism. Five treatment conditions were established: an unamended live control, a chelated metal-depleted condition, an Fe-Co-enriched treatment, a Mo-Cu-enriched treatment, and a sterilized-killed control. Microcosms were incubated under an H₂:CO₂ headspace condition at 62 °C, and changes in headspace gases and fluid chemistry were monitored over approximately nine weeks. Trace-metal availability influenced early metabolic activity across treatments. The Fe-Co-enriched treatment showed the greatest hydrogen drawdown and hydrogen sulfide accumulation, while the unamended control also produced substantial sulfide. In contrast, the chelated treatment showed minimal hydrogen consumption and negligible sulfide production, and the Mo-Cu-enriched treatment showed moderate hydrogen consumption but minimal sustained sulfide accumulation. Alkalinity increased most strongly in the Fe-Co-enriched treatment, consistent with possible metal-sulfide precipitation. Together, these preliminary results suggest that trace-metal availability can alter anaerobic redox progression in natural hydrothermal brine microcosms.